In the NTSC (National Television Standards Committee) television system, the television picture adapted for solid state sensors is comprised by a plurality of image pixels arranged in horizontal parallel rows 1-n. The image is divided into a field "A" and a field "B". Lines 1, 3, 5, etc. are first scanned and displayed in a field "A". After field "A" has been scanned, alternating lines 2, 4, 6, etc. are scanned and displayed in a field "B". Field "A" is said to be interlaced with field "B".
For compatibility reasons, the NTSC scanning method has been carried over to the still picture recording scheme. In this recording scheme, the horizontal lines from field "A" are stored in a suitable storing device such as a magnetic disc, and then the lines from field "B" are scanned and stored. The alternate field recording scheme, although satisfactory for TV camera operation, presents a problem for still picture recording.
The time separation of field "A" and field "B" in the above recording scheme creates a difficulty when an image sensor attempts to record a scene after the manner of still photography. To simulate still photography, it is necessary to take the exposure of both fields at the same time. However, for compatibility with the NTSC system and still picture storing method, the field "A" must be separately stored in the sensor, i.e., the device, from field "B" to facilitate the time sequential NTSC compatible display.
A number of designs have recently appeared in the industry to accomplish the task of making still image recording compatible with the NTSC TV system. One recent frame transfer device has a CCD imager array, an adjacent CCD memory array large enough to store both fields "A" and "B", and one-half of a CCD memory array separated by a serial readout register for the field "A" for storing field "B". The "B" field memory has its own serial readout register adjacent to it. In this frame transfer array scheme, both fields "A" and "B" are first transferred to the first memory and the line readout thereafter begins. A field "A" line is read from the first memory array, and a field "B" line is transferred through the readout register to the second, half-memory array for later readout. Fields "A" and "B" may then be read out independently while they were exposed simultaneously.
In the described device, the field "B" information must be stored in the two different locations, first in the full field memory A and B and thereafter in the half-memory B. This results in an excessively large device size that is accompanied with high device fabrication cost.
Another recent device employs an interline transfer image array and a full field memory located adjacent to the image area. In this device it is possible to transfer the lines of field "A" to the memory first and then the lines of the field "B". This results, however, in a time-delayed exposure for field "B" respective to field "A" which in turn presents a problem in recording the still pictures of imaged objects.
Conventional interline image sensors suffer from low resolution and less light sensitivity.
In view of the above, a need has arisen in the industry for a high resistivity, high-resolution image sensor that takes the same exposure for both fields at the same time and does not suffer from an inefficient utilization of the silicon chip area.